I'm sure you could get large employers (the universities for example!) to circulate/ advertise on their websites.
My suggestion for implementation (recognising you may have considered this already!)
Launch it in it's current form. I wouldn't stick posters up etc... just yet. Target specific audience(s) to testbed and get feedback. A small prize (sponsored perhaps) would pay it's way a million times over in getting people to take the time to complete a survey. Obviously the comments sections will give feedback too as you mentioned. Get buy-in sponsorship from shops, employers and use this for graphic design/website/marketing etc.... Rejig incorporating all the feedback and launch with marketing.
....or something like that :P